The basic theory and operation of thermoelectric devices has been developed for many years. Modern thermoelectric devices typically include an array of thermocouples which operate by using the Peltier effect. Thermoelectric devices are essentially small heat pumps which follow the laws of thermodynamics in the same manner as mechanical heat pumps, refrigerators, or any other apparatus used to transfer heat energy. The principal difference is that thermoelectric devices function with solid state electrical components (thermocouples) as compared to more traditional mechanical/fluid heating and cooling components.
When direct current (DC) electrical power is applied to a thermoelectric device having an array of thermocouples, heat is absorbed on the cold side of the thermocouples and passes through the thermocouples and is dissipated on the hot side of the thermocouples. A heat sink (sometimes referred to as the "hot sink") is preferably attached to the hot side of the thermoelectric device to aid in dissipating heat from the thermocouples to the adjacent environment. In a similar manner a heat sink (sometimes referred to as a "cold sink") is often attached to the cold side of the thermoelectric device to aid in removing heat from the adjacent environment. Thermoelectric devices are sometimes referred to as thermoelectric coolers; however, since they are a type of heat pump, thermoelectric devices can function as either a cooler or a heater.
There are a wide variety of containers and enclosed structures which are designed to be maintained within a selected temperature range. Examples of such containers and enclosed structures include, but are not limited to, refrigerators, picnic coolers, cabinets containing sensitive electronic equipment, and organ transplant containers. The use of thermoelectric devices which operate on a DC voltage system are well known to maintain desired operating temperatures in refrigerators and portable coolers. An example of a container having a thermoelectric cooler is shown in U.S. Pat. No. 4,726,193 entitled Temperature Controlled Picnic Box. Examples of refrigerators which function with a thermoelectric device are shown in U.S. Pat. No 2,837,899 entitled Thermoelectric Refrigerator; U.S. Pat. No. 3,177,670 entitled Thermoelectric Refrigerator; and U.S. Pat. No. 3,280,573 entitled Refrigerator--Package Arrangement. U.S. Pat. No. 5,168,339, entitled Thermoelectric Semiconductor Having A Porous Structure Deaerated in a Vacuum and Thermoelectric Panel Using P-Type and N-Type Thermoelectric Semiconductors discloses an electronic refrigeration panel.
Conventional refrigerators typically consist of an insulated enclosure with a centralized cooling system based on the vapor compression cycle of fluorinated hydrocarbons (FREON.RTM.), or other types of hydrocarbons. The cooling system usually has greater cooling capacity than the actual heat load which results in the cooling system acting intermittently in a binary duty cycle--either on or off. This binary duty cycle results in temperature variations as the refrigerator warms up while the compressor is off and cools down when the compressor is running. Thus the temperature in a typical refrigerator is not steady, but cycles between an upper limit and a lower limit. This compressor cycling may reduce the operating efficiency of the associated cooling system.
Presently available cooling systems frequently include an air/evaporator interface which requires a relatively high air flow rate to obtain the best cooling efficiency and to prevent frost or ice from forming on the evaporator. This air flow rate is often in excess of the air velocities required to cool the interior of the refrigerator and results in further system inefficiencies.
Vapor compression cooling systems frequently use CFCs (chloro-fluorocarbons) such as FREON.RTM. as the working fluid. The negative effects of CFCs on the environment are well known and there exists both national and international regulations to ban the use of such CFCs. Other fluorocarbons such as HCFCs and HFCs have their own limitations and problems for use in refrigeration systems.